It has been a desire for major meat manufacturers to supply retail outlets from centralized processing facilities. In order to facilitate this desire, modified atmosphere packaged fresh meats have been developed. Modified atmosphere packaging, also known as MAP, of fresh meats involves the use of specific gas mixtures in the headspace of gas impermeable meat containers and enables the control of certain physical properties, such as appearance, of the fresh meats for an extended period of time.
Color shelf life of red meat is important to consumer acceptance. Consumers judge the freshness of red meat by the presence of bright red oxymyoglobin pigment. Oxymyoglobin in fresh red meat decreases with time during storage as it changes to the stable brown pigment, metmyoglobin. Although oxymyoglobin pigment fades during dark storage, for example in a meat locker, pigment loss is most pronounced in lighted, refrigerated display cases in retail establishments. Although pigment loss is primarily cosmetic in nature, it has serious economic consequences. Consumers in search of the freshest looking cuts avoid purchasing red meat containing even small amounts of brown metmyoglobin. The unsaleable product which results from oxymyoglobin loss in red meats costs the industry an estimated $700 million dollars annually.
Modified atmosphere packaging can be divided into two categories, high oxygen modified atmosphere packaging having an oxygen content above 40 vol. % and low oxygen modified atmosphere packaging having an oxygen content less than 20 vol. %. In low oxygen modified atmosphere packaging, oxygen is excluded from the package and the headspace atmosphere is usually made up of an inert gas such as nitrogen or a mixture of nitrogen and carbon dioxide. With low oxygen MAP, oxymyoglobin initially present on the surface of the meat is converted to deep purple, unnatural appearing, deoxymyoglobin pigment as the last remnants of oxygen are consumed by metabolic processes occurring in the meat tissue.
Deoxymyoglobin is a fairly stable pigment under completely anoxic conditions although it can convert to metmyoglobin during storage. When oxygen is re-introduced to the meat containing deoxymyoglobin, the meat re-blooms as deoxymyoglobin is converted back into oxymyoglobin. This phenomena has been used by meat companies with so-called “peel-pack” packaging in which the meat is packaged in a tray covered by two, separate plastic films, an outer oxygen barrier film and an inner oxygen permeable film. The meat is transported and stored under anoxic conditions and, prior to display in the retail meat case, the outer film is removed to allow the meat to re-bloom and re-form the bright red pigment, oxymyoglobin, consumers expect to see. The use of “peel-pack” technology has not been embraced commercially because of the handling necessary to remove the oxygen barrier film from each package and the need to insure adequate bloom time prior to display in the retail case. The meat industry is seeking a packaging technology that can be produced at the manufacturing point, distributed and displayed at retail facilities with a minimum of handling.
In high oxygen modified atmosphere packaging, high oxygen levels are maintained in the headspace atmosphere from the time of packaging through the time of consumption. Mixtures of oxygen and carbon dioxide are typically used, with a gas mixture of 80% oxygen and 20% carbon dioxide being most typical. The high oxygen helps extend the microbial shelf life of the product by inhibiting the growth of anaerobic microorganisms, many of which are pathogens.
With both types of MAP, gas mixtures are used with carbon dioxide playing a significant functional role and other gases, particularly nitrogen, functioning as optional inert diluents. Carbon dioxide is present in the gas mixtures because at sufficient levels, it is toxic to certain bacteria and thereby enhances the product's shelf life.
Modified atmosphere packaging has provided a method of extending the favorable appearance and properties of fresh meat but there still is a need for a method of further extending the packaged appearance of fresh meats.
W. Manu-Tawiah, L. L. Ammann, J. G. Sebranek and R. A. Molins, 1991. “Extending the Color Stability and Shelf Life of Fresh Meat,” Food Technology 45(3), 94–102, teach that mixtures of tetrasodium pyrophosphate, sodium erythrobate and citric acid combined with modified atmosphere storage extended the color life of various meat types and cuts. The headspace atmosphere used in this work was 50% CO2, 15% O2 & 35% N2. Pork chops, beef rib steaks, and ground beef samples were examined. Treatment suspensions were applied by marination of prime cuts and by direct addition to ground beef prior to the final grind. Samples were stored at 2° C. in cardboard boxes for 0, 7, 14, 21, or 28 days prior to opening. After master batch storage, individual trays were stored at 2° C. under fluorescent light for 0, 2, 4, 6, 8, or 10 days. Very little effect was seen on pork. Ground beef showed the most improvement with shelf life being extended by 1–3 days. In contrast, steaks gained one day of shelf life while no improvement was seen for chops. The greatest color differences occurred after 7 days dark storage and 3 days storage in the light. Erythrobate was shown to have significant effects on color in beef and to effect TBAs favorably. Sensory panelists were unable to distinguish between treated and untreated materials at any stage.
C. Faustman, W. K. M. Chan, M. P. Lynch and S. T. Joo, 1996, “Strategies for Increasing Oxidative Stability of (Fresh) Meat Color.” Reciprocal Meat Conference Proceedings, 49, 73–79 teach that adding water soluble antioxidants such as ascorbic acid to meat preserves red meat color. Oxymyoglobin is more stable in meat with higher tocopherol concentrations. This work did not involve MAP technology. The authors also reviewed work showing that modified atmosphere packaging was an effective tool for extending color life. These authors showed that meat stored in MAP which contained sachets of iron (an oxygen scavenger) demonstrated significantly greater retail color shelf life than those which were not exposed to oxygen scavengers.
S. D. Shivas, H. H. Kropf, M. C. Hunt, M. C. Kastner, L. L. A. Kendall and D. A. Dayton, 1984. “Effect of Ascorbic Acid on Display Life of Ground Beef,” J. Food Protect. 47, 11–15, 19, disclosed that ascorbic acid levels at 0.05 and 0.1% prolonged display life of 20 and 25% fat grade ground beef, with 25% fat content beef giving higher scores. Beef flavor improved with ascorbic acid treatment while TBA values decreased with ascorbic acid treatment. Display life was extended by 5 days. This work did not involve MAP technology.
B. E. Greene, I.-M. Hsin and M. W. Zipser 1971, “Retardation of Oxidative Color Changes in Raw Ground Beef.” J. Food Sci. 36, 940–942, treated ground beef with ascorbic acid plus either BHA or propyl gallate. Treatment was shown to effectively retard oxidation for up to eight days of refrigerated storage. This work did not involve MAP technology.
Chin S. Cheng, U.S. Pat. No. 4,683,139, Jul. 28, 1987, teaches a process for preserving color in fresh pork using a phosphate, ascorbic acid or iso-ascorbic acid and a chelator (EDTA, citric or tartaric acid) in combination with modified atmosphere packaging. The treatment extended color shelf life up to 21 days. The atmosphere used in this work ranged from about 2% to about 30% oxygen.
T. Okayama 1987, “Effect of Modified Gas Atmosphere Packaging After Dip Treatment on Myoglobin and Lipid Oxidation of Beef Steaks.” Meat Sci. 19, 179–185 dipped beef steaks in an ethanolic solution of ascorbic acid and tocopherol. The MAP (80% O2, 20% CO2) steaks with or without dip treatment maintained acceptable color after 13 days of storage. Dip treatment showed no significant improvement in color. TBA numbers of samples stored in air or under 80% O2, 20% CO2 atmosphere were lower for the dip treated samples than for the non-dip treated samples.
Allen, P., Doherty, A. M., Buckley, D. J., Kerry, J., O'Grady, M. N., Monahan, F. J. 1996, “Effect of oxygen scavengers and vitamin E supplementation on colour stability of MAP beef,” 42nd In. Cong. Meat Sci. Technol., 88–89, teaches that supplementation of the diet of steers with 2000 units of vitamin E (tocopherol) per day for forty days prior to slaughter had no effect on color stability of steaks stored with or without iron-containing oxygen scavengers in an atmosphere of 50% carbon dioxide; 50% nitrogen.
Sante, V., Renerre, M., Lacourt, A., J. Food Qual. 17 177–195, discusses the effect of modified atmosphere packaging on color stability and on microbiology of turkey breast meat. The best color results were obtained using a 100% carbon dioxide atmosphere combined with an oxygen scavenger. This treatment outperformed atmospheres containing high levels of oxygen.
J. H. Hotchkiss et al, “Advances in and Aspects of Modified Atmosphere Packaging in Fresh Red Meats”, Reciprocal Meat Conf. Proc. 42 (1989), pages 31–40, states that although rosemary has been added to MAP poultry to preserve the color thereof, “Fortunately for the poultry people, poultry is not judged for myoglobin, so color is not a serious problem.”
Yukichi Kimura et al, U.S. Pat. No. 4,380, 506, Apr. 19, 1983, discloses the addition of extracts of herbs such as sage, rosemary, marjoram, thyme, oregano and basil to food products such as ham, sausage and processed marine and livestock products for their antioxidant and anti-bacterial properties.
Uy Nguyen et al, U.S. Pat. No. 5,017,397, May 21, 1991, discloses plant extracts which are obtained by supercritical fluid extraction of ground leaves of the Labiatae family and added to food products such as processed meats and fish for their antioxidant properties. They do not discuss red meats.
Paul H. Todd, Jr., U.S. Pat. Nos. 5,061,403 and 5,209,870, Oct. 29, 1991 and May 11, 1993, both disclose a process for preparing an alkaline solution of Labiatae antioxidants and the use of these antioxidants in combination with polyphates in the pumping or brining of meats to inhibit “warmed-over” flavor and prevent off-color development.
Souzan Saad Latif Abd. El-Allm et al, Culinary herbs inhibit lipid oxidation in raw and cooked minced meat patties during storage”, J Sci Food Agric (1999), Vol. 79, pages 277–285, disclose the mixing of spice extracts, such as sage, basil, thyme and ginger, with ground pork pretreated with an aqueous salt solution to prevent lipid oxidation.
F. Timmermann, “Effectiveness of Natural Antioxidants in Salami-type Sausages”, Oils-Fats-Lipids (1975), Vol. 2, pages 351–353, discloses the use of natural antioxidants such as tocopherols or spice extracts in prolonging the shelf life of animal fats and cured raw sausages.
Although the prior art discussed above shows different methods of reducing oxidation effects in meats, particularly in the presence of oxygen scavengers and in inert atmospheres, this work is directed primarily at cured meats, or fresh red meat packaged under low (<30%) oxygen containing atmospheres. Only one author, Okayama, examined fresh red meat stored under a high oxygen atmosphere and his dip treatment was found to be ineffective in improving color. The prior art does not adequately address the problem of color retention in fresh red meats, and the need for a safe, permissible, and effective method of extending color life of prepackaged red meats remains. There still exists a need for a method of greatly extending the color life of modified atmosphere packaged fresh red meat, including meat that has not been subjected to a chemical processing or pretreatment step, through the use of a natural treating agent. While the prior art used oxygen scavengers such as ascorbates and erythrobates to prolong color shelf life, these are not permissible additives to red meats. The combination of these scavengers with conventional antioxidants, such as the synthetics BHA and BHT, and tocopherol, would be expected to slow down lipid oxidation. However, none of these conventional lipid antioxidants are permissible additives in red meats. Consequently, this invention provides the only presently known legal means of extending the color shelf life of MAP red meats.